The invention relates generally to loudspeakers and particularly to an improved multidriver loudspeaker.
Ideally, a loudspeaker-driver should be capable of reproducing all frequencies so that the source of, for example, the high and low frequency sound waves is a single location. This would result in the time and phase coherence of all sound waves, thereby producing undistorted natural sound. It is difficult, however, to build a conventional driver that is both big enough to reproduce the low frequencies and light enough to reproduce the high frequencies. Therefore, most loudspeaker systems utilize two or more drivers and are termed multidriver loudspeaker. Several major problems arise when multiple drivers are used in a single loudspeaker. Specifically, at some frequencies several drivers are functioning and the actual location of the sound is not fixed for the listener. In addition, as the listener moves around the listening area, the distance from each driver to the listener changes in a non-uniform manner, such that at one location the listener is closer to the low frequency driver and at a second location the listener is closer to the high frequency driver. This results in the non-synchronization of the wave fronts reaching the listener at all frequencies. Finally, at the crossover point, where both drivers are producing the same amount of output, phase shifts will exist between the sound waves emanating from the two drivers caused by the difference in path lengths from the drivers to the listener. To a great extent, these problems are inherent in any multidriver loudspeaker system and are caused by the fact that the apparent or virtual acoustical source of the drivers are not all at the same location. The apparent or virtual acoustical source of a driver is the point in space where the sound wave front from the driver appears to a listener to originate at the time the input is applied to the driver. Typically, in view of the inertial characteristics of the driver, the apparent acoustical source of a driver is behind the voice coil--cone junction and within the magnetic structure of the driver.
Obviously, if the apparent acoustical source for all of the drivers were the same point in space many of the problems described above would be solved. In fact, several complex mechanical structures have been developed in an attempt to achieve this, resulting in the embedding of the high frequency driver inside the magnetic structure of the low frequency driver. Practically, these speakers are too expensive to manufacture and as such, are not manufactured. Further, even if speakers of this type could be manufactured at a reasonable cost, they incorporate other disadvantages since the sides of a low frequency driver tend to act somewhat like a horn with respect to the sound emanating from the low frequency driver (horn loading) thereby distorting the sound produced thereby.
Ohter attempts to solve the problems inherent in multidriver loudspeakers include positioning the high frequency driver in front of the low frequency driver. This solution is unsatisfactory as it creates a constant time delay in the sound waves emanating from the low frequency driver which becomes acute at the crossover of the two drivers. Further, the high frequency driver in such an arrangement serves as a diffracting object and interferes with the second produced by the low frequency driver.